Create check-if-word-is-valid-after-substitutions.cpp

Author: kamyu104

C++/check-if-word-is-valid-after-substitutions.cpp

@@ -0,0 +1,25 @@
+// Time:  O(n)
+// Space: O(n)
+
+class Solution {
+public:
+    bool isValid(string S) {
+        string stack;
+        for (const auto& c : S) {
+            if (c == 'c') {
+                if (stack.size() >= 2 &&
+                    stack[stack.length() - 2] == 'a' &&
+                    stack[stack.length() - 1] == 'b') {
+
+                    stack.pop_back();
+                    stack.pop_back();
+                } else {
+                    return false;
+                }
+            } else {
+                stack.push_back(c);
+            }
+        }
+        return stack.empty();
+    }
+};